The development and performance of typewriting were studied by collecting data from 18 typists. They ranged from beginning students in a typing class (about one keystroke per second) to expert professional typists (about 10 keystrokes per second). All typists became faster with practice, but the rate and amount of improvement varied for different classes of keystroke sequences. The pattern of keystroke times displayed qualitative changes with the development of typewriting skills. The correlation between successive interstroke intervals of some letter sequences became more negative for the more expert typists. In addition, the relative variability of the interstroke intervals decreased with learning. These experimental findings were interpreted as being due to two general development changes: the finger movements become less sequential and more overlapping with practice and performance shifts from being limited by cognitive constraints in students to being limited by motoric and physical constraints in experts. (YLB)